It is common in many types of wireless communications (e.g., Wi-Fi, long term evolution (LTE), evolved high speed packet access (HSPA+), WiMax, etc.) for multiple-input multiple-output (MIMO) wireless systems to be used to improve performance. With MIMO, multiple antennae are used at each end of the wireless link to spatially multiplex data streams.
MIMO performance is improved by using an iterative detection-decoding (IDD) system to reduce the signal-to-noise ratio (SNR) required for a reliable transmission. An IDD system generally comprises a soft-in soft-out (SISO) detector and a SISO forward error correction (FEC) decoder. The detector is operable to cancel interference, and the decoder is operable to correct errors. Collectively, the detector and decoder exchange soft information in an iterative manner to improve SNR. Detectors used in known or conventional IDD systems include spherical detectors (SD) and minimum mean square error (MMSE) detectors, with MMSE detectors being less complex and easier to scale up to support high data rates and spectral efficiency. Decoders used in known or conventional IDD systems include binary low-density parity-check (LDPC) decoders.
In addition to the detector and decoder, the IDD system also includes an interface between the detector and decoder that is operative to convert the output of the detector (soft symbol and variance) to the input of the decoder (a priori log likelihood ratio (LLR)), and output of the decoder (a posteriori LLR) to the input of the detector (soft symbol and variance). This can be done in the binary domain or nonbinary domain, wherein in the binary domain, the conversion between symbol statistics and LLR is done on a bit-by-bit basis.
The use of nonbinary code, e.g., nonbinary LDPC, and a nonbinary decoder can provide better coding gain and improved detection-decoding performance as compared to binary code, e.g., binary LDPC, and a binary decoder. However, the bit-by-bit conversion between symbol statistics and nonbinary LLR using a conventional binary interface is inefficient.
Accordingly, there is a need for a nonbinary interface for use between a detector and decoder of an IDD system that minimizes and/or eliminates one or more of the above-identified deficiencies.